Since the beginning of oil production from subsurface formations, the industry has been concerned with efficient control of the movement of unconsolidated formation particles, such as sand, into the wellbore. For example, such particle movement commonly occurs during production from completions in loose sandstone or following hydraulic fracture of a formation. Production of these materials causes numerous problems in the operation of oil, gas or water wells. These problems include plugging of formations, tubing and subsurface flow lines, as well as erosion of tubing, downhole equipment and surface equipment. These problems lead to high maintenance costs and unacceptable well downtime. Accordingly, numerous methods have been utilized to control the movement of unconsolidated particles during the production of fluids.
Gravel packing is commonly used to prevent the production of sand. Generally, gravel packing involves placing pack sand, an aggregate or particulate material, in the annular space between the wellbore and a fluid permeable, perforated base pipe that is located adjacent to the production zone. A particular pack sand is selected to prevent the flow of formation particles therethrough, taking into consideration the characteristics of the particular reservoir. The perforated base pipe is designed to allow hydrocarbon liquids and gases to flow therethrough with minimum resistance. Gravel packing is commonly achieved by either an open hole gravel packing procedure or an internal gravel packing procedure, depending on the characteristics of the particular reservoir.
In addition to the use of a perforated base pipe and gravel packing, a sand control screen is commonly employed to control the movement of formation particles. These screens may comprise a continuous single screen wire that is wrapped around the base pipe. While this type of screen is capable of excluding even the smallest API grades of pack sand, these screens are easily damaged during handling, installation and production.
More recently, a sand control screen comprising a sand control screen jacket has been used. The screen jacket is fully formed from a single screen wire wrapped around a plurality of ribs that extend longitudinally along the internal surface of the screen jacket to provide strength to the screen wire and stand-off between the screen wire and the base pipe once the screen jacket is attached to the base pipe. In addition, some screen designs use prepacked sand confined around the perforated base pipe. These prepacked screens are constructed by fabricating the metal components, then forcing pack sand, either resin coated or uncoated, between the perforated base pipe and a single wire screen or between an inner wire screen and an outer wire screen of a multi-layer screen.
It has been found, however, that whether single or multi-layer, conventional or prepacked, the screen wire of sand control screens are susceptible to corrosion. Specifically, environmental cracking has occurred in the screen wire, which is the formation of brittle cracks in the screen wire material, such as a stainless steel alloy. Environmental cracking includes, for example, stress corrosion cracking. Stress corrosion cracking typically occurs as a result of contact between sand control screens made from a susceptible alloy and a halide environment which is present, for example, in saltwater or is introduced by virtue of acidizing the well.
In addition to halide ion concentration, stress corrosion cracking of materials, such as a stainless steel alloy, also depends upon the pH of the environment, the magnitude of tensile stress in the metal, time and the temperature. For example, an environment having a high halide concentration, a low pH and a high temperature promotes stress corrosion cracking of certain alloys such as the aforementioned stainless steel. This type of corrosive environment is commonly encountered by a sand control screen once it is placed downhole.
It has been found, however, that the nickel concentration in the metal alloy of the screen wire greatly affects the likelihood of stress corrosion cracking. For example, alloys having less than approximately 42% nickel, such as the most frequently used austenitic stainless steels, types 304, 304L and 316L, are susceptible to stress corrosion cracking. On the other hand, alloys having a high content of nickel, such as Incoloy 825 having approximately 42% nickel, are highly resistant to stress corrosion cracking. As such, materials such as Incoloy 825 have been used for the screen wire of sand control screens to overcome the problem of environmental cracking. The cost of exotic materials such as Incoloy 825, however, is between three and eight times that of stainless steels.
Therefore, a need has arisen for a sand control screen for filtering particles out of fluid produced from a wellbore that is capable of withstanding the severe downhole conditions encountered during installation, production, acidizing and the like. A need has also arisen for such a sand control screen that will not suffer from environmental cracking in an environment having a high halide concentration, a low pH and a high temperature. Additionally, a need has arisen for such a sand control screen that does not require the use of exotic alloys such as Incoloy 825 but instead utilizes less expensive materials for the screen.